STYLE: Prefer C++11 zero initializer to ZeroValue

[hjmjohnson]

Prefer to use standard C++ language initializers to the itk::NumericValues<>::ZeroValue() initializers.

PR Checklist

• No API changes were made (or the changes have been approved)
• No major design changes were made (or the changes have been approved)

[thewtex]

👍

[N-Dekker]

Wonderful, thanks Hans! Did you use a regular expression to find and replace all those cases? If so, can you possibly still share the regular expression, either in the commit message or as a PR comment?

BTW, I would slightly reword the subject line, to mention {} explicitly, for example:

STYLE: Prefer C++11 `{}` initializer to NumericTraits::ZeroValue() call

But that's just a matter of style 😸 Approved anyway! 👍

[blowekamp]

Will the {} initializer work for non-scalar pixel types too? Does this add new requirements for pixel types? As I recall some multi-component types itk::Size or itk::Index were defined as aggregate types. Will the {} initialization still zero the components?

[N-Dekker]

Will the {} initializer work for non-scalar pixel types too? Does this add new requirements for pixel types? As I recall some multi-component types itk::Size or itk::Index were defined as aggregate types. Will the {} initialization still zero the components?

Hi @blowekamp Yes, itk::Size<N> and itk::Index<N> are properly zero-initialized by {}.

[N-Dekker]

@blowekamp To elaborate on your question, with the following user-defined types (below here), the data members of instances of Aggregate and DefaultedConstructor are properly zero-initialized by the form T var{}. Only EmptyConstructor::m_Data3 is not initialized by EmptyConstructor var{}.

struct Aggregate
{
    int m_Data1;
};

class DefaultedConstructor
{
public:
  DefaultedConstructor() = default;
  int m_Data2;
};

class EmptyConstructor
{
public:
  EmptyConstructor() {}
  int m_Data3;
};

Aggregate aggregate{};  // m_Data1 is zero-initialized.
DefaultedConstructor defaultedConstructor{};  // m_Data2 is zero-initialized.
EmptyConstructor emptyConstructor{};  // m_Data3 is uninitialized!

See https://godbolt.org/z/xodK1T5Ys